I have some gashes in my sub-floor that I'd like to fill/level before placing laminate flooring down. Upon checking at my local home depot, I found some floor leveling compound but quite frankly, I'm scared to use it. There are very large warnings on it confirming that the contents of it are a known carcinogen and shouldn't be inhaled, touched, etc.

Now obviously I'm going to be wearing all required safety equipment but I'd much rather use something a little less toxic. Is there anything else I can use to level-out small imperfections in my sub-floor?

3 Answers
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If the gashes you describe are not large, say more than 1/4 inch deep or more than say 6inX6in in size, don't worry about them. go right over them. If you really feel that they need to be filled, use the floor leveler. it does contains silicates which is only harmful in a dry dust state, and then only if you live in the stuff for a long long time. Once it is wetted/mixed and on the floor , there is no danger if you don't go crazy sanding it. You can also use regular drywall compound or quick set if you have the patience to wait for it to dry before starting your floor.

wood subfloor? can you cut out the bad sections and replace it with new plywood?

if you do this, i would recommend installing some 2x4's underneath the section you cut out, perpendicular to the stringers. install them so they cover the joint between the old and new subfloor. depending on the size of the patch, you might also want to support it somewhere in the middle. and then also install 2x4's along the edges of the patch parallel to the stringers.

below is a drawing that show's what i'm talking about. it's a bottom-up view of the subfloor. the part you're cutting out is in red, and the 2x4's you're installing are in green. i did not draw in the parallel 2x4's i recommended above.

Is it safe to assume that the subfloor is concrete? Depending on the size of the gashes, you'd have a couple of options.

First option would be to simply ignore them. There are different types of material you can place under laminate flooring, and you might be able to get away with just putting down a heavy duty foam underlayment.

The next option would be to put down something like this - again, you're not going to have to worry about any gashes in the subfloor.

Finally, you could consider putting in some self-leveling concrete if it's really, really bad - but that would probably be the most expensive, and the most work.

Update:

Given that the subfloor is wood, probably the best bet is to put down plywood over the existing floor. You can glue it to the existing subfloor, plus screw it into the joists, which will give you a nice flat surface for the new flooring, plus it should eliminate squeaking. If height is an issue (i.e. you're trying to match up the new floor level with an existing floor, you can try using 1/4" plywood.